The Magpie is one of the most intelligent birds, and it is believed to be one of the most intelligent of all animals. The expansion of its neostriatum is approximately the same in its relative size as is found in chimpanzees, orangutans and humans.

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The Magpie is 44–46 centimetres (17–18 in) in length - in the adult over 50% of this is tail - and a wingspan of 52–62 centimetres (20–24 in). Its head, neck and breast are glossy black with a metallic green and violet sheen; the belly and scapulars (shoulder feathers) are pure white; the wings are black glossed with green or purple, and the primaries have white inner webs, conspicuous when the wing is open. The graduated tail is black, shot with bronze-green and other iridescent colours. The legs and bill are black.

The young resemble the adults, but are at first without much of the gloss on the sooty plumage. The male is slightly larger than the female.

The Magpie is a distinctive species with its pied plumage, long 20–30 centimetres (8–12 in), graduated tail and loud chatter. When Magpies pass each other in open country, they command attention by rapidly moving their wings and chattering. When the bird lands, the long tail is elevated and is carefully carried clear of the ground.

Like other corvids, such as crows, the Magpie usually walks, but it can also hop quickly sideways with wings slightly opened. The Magpie and the rest of its family are fond of bright objects.

The Magpie will eat any animal food. These foods include young birds and eggs, insects, scraps and carrion. The bird will also eat acorns, grain and other vegetable substances.

Magpies are common to suburban areas but can be more shy and cautious in country areas. The birds do not avoid humans unless they are harassed. Sometimes two or more birds display "teasing" behaviour towards animals such as cats. It is thought that this behaviour may be to scare away potential predators and egg thieves.

In winter, Magpies often form groups to feed and roost at night. Early in the year, large numbers collect together for mating in gatherings Charles Darwin described as "marriage meetings".

The magpie has been observed taking small songbirds down in flight. This behaviour was once thought to occur only in birds of prey.

The Magpie is believed to be among the most intelligent of birds, and among the most intelligent of all animals. Magpies have been observed engaging in elaborate social rituals, possibly including the expression of grief. Mirror self-recognition has been demonstrated in magpies. The magpie is thus one of a small number of species, and the only non-mammal, known to possess this capability. The cognitive abilities of the Magpie are taken as evidence that intelligence evolved independently in both corvids/crows and primates. This is indicated by feats such as tool use, their ability to hide and store food across seasons, episodic-like memory, and the ability to use one's own experience in predicting the behavior of conspecifics. Various behaviours have been observed that indicate intelligence. It has been observed that they cut up their food in correctly sized proportions, depending on the size of their young.

In captivity magpies have been observed counting up to get food, imitating human voices, and regularly using tools to clean their own cages. In the wild, they organise themselves into gangs, and use complex strategies when hunting other birds, and when confronted by predators. Along with the Jackdaw, the Magpie has been found to have a neostriatum approximately the same relative size as is found in chimpanzees and humans, and significantly larger than is found in the gibbon. Like other corvids, such as Ravens and Crows, their total brain to body ratio is equal to that of great apes and cetaceans, and only slightly lower than in humans.

Magpies are territorial and stay in their territory all year, even in north of the species range. The pairs are monogamous, and remain together for the duration of their lives. Should one of the two die, the widow or widower will find a new partner from the stock of yearlings.

Mating takes place in spring. In the courtship display, the males rapidly raise and depress their head feathers, uplift, open and close their tails like fans, and call in soft tones quite distinct from their usual chatter. In the display the loose feathers of the flanks are brought over and the primaries, and the patch on the shoulders is spread so as to make the white conspicuous, presumably to attract the female eye. Short buoyant flights and chases are part of the courtship.

Tall trees are selected by the Magpie for its bulky nest; it is firmly attached to a central fork in the upper branches. The framework of the sticks is cemented with earth and clay, and a lining of the same material is covered with fine roots; above is a stout though loosely built dome of prickly branches with one well-concealed entrance. When the leaves fall these huge nests are plainly visible. Where trees are scarce, and even in well-wooded country, nests are at times built in bushes and hedgerows.
The eggs, small for the size of the bird, number from five to eight, and as many as ten are recorded; they show much variation in ground and marking, but a usual type is blue-green with close specks and spots of brown and grey. They are laid in April, and only one brood is reared unless disaster overtakes the first clutch.